FIX: Use colormap objects in rcParams when setting cmap

greglucas · greglucas · commit 40a321f86cf3 · 2023-03-16T15:25:29.000-06:00
image.cmap previously used a string, which would lookup that
string in the colormap registry. This caused issues if there was a
mismatched registration name versus attribute name. Instead if
we get a colormap object, we should just use that directly rather
than using any name to look things up.
diff --git a/lib/matplotlib/cm.py b/lib/matplotlib/cm.py
@@ -715,9 +715,9 @@ def _ensure_cmap(cmap):
     Colormap
 
     """
-    if isinstance(cmap, colors.Colormap):
-        return cmap
     cmap_name = cmap if cmap is not None else mpl.rcParams["image.cmap"]
+    if isinstance(cmap_name, colors.Colormap):
+        return cmap_name
     # use check_in_list to ensure type stability of the exception raised by
     # the internal usage of this (ValueError vs KeyError)
     _api.check_in_list(sorted(_colormaps), cmap=cmap_name)
diff --git a/lib/matplotlib/pyplot.py b/lib/matplotlib/pyplot.py
@@ -2180,13 +2180,10 @@ def set_cmap(cmap):
     matplotlib.cm.register_cmap
     matplotlib.cm.get_cmap
     """
-    # The name of the colormap may be different than the registered name.
-    # We want the registered name for the rc setting
-    name = getattr(cmap, "name", cmap)
-    # Run the cmap (str or Colormap) through get_cmap to validate
-    # the cmap before updating the rc parameters
+    # Run the cmap (str or Colormap) through get_cmap to validate the cmap
+    # and get an instance of Colormap before updating the rc parameters
     cmap = get_cmap(cmap)
-    rc('image', cmap=name)
+    rc('image', cmap=cmap)
     im = gci()
 
     if im is not None:
